Livestock models for exploiting the promise of pluripotent stem cells.

Livestock species are widely used as biomedical models. Pigs, in particular, are beginning to have a significant role in regenerative medicine for testing the applicability, success, and safety of grafts derived from induced pluripotent stem cells. Animal testing must always be performed before any clinical trials are performed in humans, and pigs may sometimes be the species of choice because of their physiological and anatomical similarities to humans. Induced pluripotent stem cells (iPSC) have been generated with some success from livestock species by a variety of reprogramming procedures, but authenticated embryonic stem cells (ESC) have not. There are now several studies in which porcine iPSC have been tested for their ability to provide functional grafts in pigs. Pigs have also served as recipients for grafts derived from human iPSC. There have also been recent advances in creating pigs with severe combined immunodeficiency (SCID). Like SCID mice, these pigs are expected to be graft tolerant. Additionally, chimeric, partially humanized pigs could be sources of human organs. Another potential application of pluripotent stem cells from livestock is for the purpose of differentiating the cells into skeletal muscle, which, in turn, could be used either to produce cultured meat or to engraft into damaged muscle. None of these technologies has advanced to a stage that they have become mainstream, however. Despite the value of livestock models in regenerative medicine, only a limited number of institutions are able to use these animals.